Electrical engineering calculators
A growing collection of fast, accurate calculators for electricians, electronics hobbyists and EE students. Every tool runs instantly in your browser.
Basics & Ohm's law
The core electrical relationships — Ohm's law, power, and how voltage and current divide in a circuit. The starting point for almost every other calculation.
Ω Ohm's Law
V, I, R, P from any two.
🔁 Watts / Volts / Amps
Convert between W, V and A for DC and AC.
➗ Voltage Divider
Output voltage from two resistors.
🔀 Current Divider
Split a current between two parallel resistors.
Resistors & capacitors
Read resistor and capacitor codes, pick the right series resistor for an LED, and combine components in series or parallel.
🎨 Resistor Color Code
Decode 4, 5 and 6-band through-hole resistors.
🔠 SMD Resistor Code
Decode 3-digit, 4-digit and EIA-96 SMD codes.
🔢 Capacitor Code
Decode 3-digit ceramic capacitor codes.
💡 LED Resistor
Find the correct series resistor for any LED.
🔌 Series / Parallel Resistors
Total resistance of any combination.
🔋 Series / Parallel Capacitors
Total capacitance of any combination.
Power, wiring & mains
Size cables and conduit, work out voltage drop, three-phase power, transformer and motor ratings. Always check a final design against your local electrical code.
📉 Voltage Drop
Voltage drop and % drop for a cable run.
🧵 Wire Size (AWG)
Minimum copper/aluminum conductor for a current.
⚙️ Three-Phase Power
kW, kVA, amps and power factor.
📐 Power Factor Correction
Capacitor kVAR needed to correct power factor.
🔌 Energy Cost
Running cost of any appliance per day, month, year.
🔁 kVA / kW / Amps
Convert between kVA, kW and current (1Ø/3Ø).
🔌 Transformer Sizing
Required transformer kVA and full-load current.
🌀 Motor Full-Load Current
FLA for single- and three-phase motors.
🧰 Conduit Fill
Minimum EMT/PVC/RMC size per NEC.
📊 Main Panel Capacity
Service capacity vs demand load and spare.
Home heating & EV
Size electric heating and EV charging for a home — sauna heaters, room and underfloor heating, charging time and peak demand.
♨️ Sauna Heater Size
Recommended sauna heater power from room volume.
🔥 Room Heating Power
Watts needed to heat a room electrically.
🌡️ Underfloor Heating Cable
Floor heating power, cable length and spacing.
🚗 EV Charging Time
How long to charge an electric car battery.
🏠 Peak Power & Main Fuse
Peak kW to current, fuse size and tariff step.
❄️ Heat Pump Load
Electrical input power and breaker for a heat pump.
Solar, battery & EV
Plan solar, battery and EV installs: backup runtime, low-voltage DC cable sizing, charger load sharing and charging cost.
🔋 Battery Backup Runtime
How long a home battery powers your loads.
☀️ 48V Inverter Cable Size
DC cable cross-section for a battery/inverter run.
⚖️ EV Charger Load Sharing
Spare current and power per EV charger.
💰 EV Charging Cost
Cost to charge an EV and off-peak savings.
Electronics design
Design small electronics circuits — RC filters, 555 timer stages and battery runtime.
〰️ RC Filter Cutoff
Cutoff frequency and time constant of an RC filter.
⏱️ 555 Timer
Frequency, period and duty cycle (astable/monostable).
🔋 Battery Life
Runtime from capacity (mAh) and load current.
About these calculators
VoltCalc brings common electrical and electronics calculations into one fast, clean place. Whether you're sizing a cable, filling a conduit, picking a resistor for an LED or working out three-phase current, each tool shows the formula it uses so you can check the result. Everything runs in your browser — no sign-up, no waiting.
The tools are built for electricians and apprentices, electronics hobbyists and makers, and engineering students — anyone who needs a quick, trustworthy number without installing software or creating an account.
Results are estimates for learning and planning. Electrical work is governed by local codes (such as the NEC and IEC) and can be dangerous, so always verify a final design and have it checked by a qualified electrician. Our methodology and disclaimer pages explain the formulas, data sources and limits behind each tool.